1. Field of the Invention
The present invention relates to an apparatus for discontinuous withdrawing of a cast strand from a continuous casting mold, in particular from a horizontal continuous casting mold having at least two drive rollers which can be pressed against two oppositely disposed strand sides and which drive rollers are driven by a drive.
2. Brief Description of the Background of the Invention Including Prior Art
It is known from (DE-AS 1 783 032) to withdraw the strand stepwise from the horizontal continuous casting mold with discontinuously driven rollers, where the continuous casting mold is disposed stationary during the casting, i.e., it does not oscillate. In contrast, the strand performs a discontinuous relative movement with respect to the horizontal continuous casting mold based on the forces transmitted to it by the drive rollers. The drive for discontinuously driven rollers is very expensive, in particular if the strand must not only perform a movement in the casting direction, but also a movement between the withdrawal steps of about a fraction of a length of a casting step against casting direction of the continuous casting mold. The length of the withdrawal steps must be variable in accordance with the solidification conditions, so that the control for the drive of the drive rollers is complex and expensive.
From the German Patent Application Laid Open DE-OS No. 1 583 611 it is known to drive the drive rollers of a horizontal continuous casting machine continuously and to periodically clamp the strand in a stationary position with a clamping device. During this clamping process the drive rollers roll along the surface of the strand and change their position with respect to the strand corresponding to this rolling, i.e., the axes of the drive rollers perform an oscillating movement. For this purpose the drive roller frame is mounted on a slide carriage, where the slide carrier is slidable and driven with a pressure medium cylinder. This construction is disadvantageous since a control device for clamping the strand with the clamping device must be provided in addition to the drive for the slide carriage and the drive for the drive rollers. The slide guides for the drive roller frame require particular attention, since slide guides in continuous casting mold installations tend to accumulate dirt and always represent an increased risk factor for the operating safety. Moreover, it is not possible to push back the strand against the casting direction between the withdrawal steps with the installation known from DE-OS No. 1,583,611 such a push-back, however is often required for the optimum formation of the strand shell.